This invention relates generally to earth well drilling apparatus and methods. Particularly it relates to apparatus and methods applicable to drilling one or more bore holes in a mineral bearing formation using multiple hydraulic forces.
A conventional drill hole for producing oil from an oil-bearing formation is formed by drilling with a bit driven by a rotating drill pipe which extends through the central opening of a well. A drilling fluid is passed centrally through the drill pipe to remove the cuttings in the excavated area ahead of the bit to form a slurry which is pumped to the surface in an annular space formed between the drill pipe and adjacent earth formation. After drilling, a casing is placed into the bore hole and cemented to the formation.
There are a number of disadvantages in the use of the foregoing technique. Firstly, it is expensive to drill into the earth with a rotating drill system at extended depths. Secondly, it is difficult to change the direction of the drilling from vertical to horizontal, as would be desirable for efficient production of petroleum in some situations. Thirdly, the rotation of the drill pipe to which the bit is attached within the casing creates great friction, power loss, and wear of both drill pipe and casing.
By the use of known whipstock devices and techniques, a bore hole may be directed laterally from the vertical. However, transition from a vertical to a horizontal bore hole presents difficulties, particularly when a small turning radius is desired (e.g. less than a ten foot radius), to permit injection of steam, solvents or other fluids into the formation for enhanced recovery of minerals. This capability is particularly desirable for heavy (high viscosity) oil-bearing formations.
A number of techniques have been attempted to form lateral or radial (essentially horizontal) bore holes from a vertical, cased bore hole. In one technique, an oversized vertical bore hole is formed of sufficiently large diameter such that miners may descend to a location bear the bottom of the hole, from which they can drill horizontal holes by conventional means. This technique is both costly and dangerous, particularly at great depths. In another approach, a technique known as drain-hole drilling is employed. Here, a vertical bore hole is bored with rotary equipment in a conventional way. A special assembly is attached near the lower end of the drill column, including a pre-formed, non-rotating, curved guide tube known as a whipstock, and an inner, flexibly jointed, rotatable drive pipe. Then, the drill passes along the curved assembly in a generally lateral direction to drill a lateral. A variety of such systems are set forth in the following U.S. Pat. Nos. 2,669,429, Zublin Feb. 16, 1954; 2,797,893, McCune et al. July 2, 1957; and 3,398,804, Holbert Aug. 27, 1968. Multiple whipstocks for directing drill pipes at oblique angles are suggested in Owsley et al., U.S. Pat. No. 3,330,349, July 11, 1962. All of these systems are subject to the disadvantage that there is a high frictional relationship between the curved, flexibly jointed drill pipe and the adjacent formation, and it is difficult to form truly horizontal bore holes; instead, downwardly directed bore holes with relatively large turning radii are formed. In some instances horizontal bore holes have been drilled, but with the use of whipstock means which applies a relatively large radius turn or bend. In additon, such bore holes are costly to drill and directional control is erratic. Another disadvantage is that the deflected rotating drill pipe tends to wear out quickly due to continuous frictional contact with the formation. In addition, the friction between the deflected rotating drill pipe and the formation limits the extent to which the drill can penetrate the formation before being stopped.
A variant of the drain-hole principle for subterranean boring is disclosed in Grebe U.S. Pat. No. 2,271,005, Jan. 23, 1939. There, a flexible drilling conduit terminating in an elongate bullet-shaped hydraulic drillhead with multiple ports passes through a curved guide tube. A hydraulic fluid, such as acid solution, is pumped through the conduit from the surface of the well and discharged from the drilling head to form a radially directed bore as the drilling head is advanced. A complex system is disclosed for driving the conduit incrementally forward by the application of force thereto and by periodic inflation and deflation of inflatable packers spaced in the conduit. The resulting discontinuous creeping movement of the conduit is analogous to that of an earth worm.
A system somewhat similar to the aforementioned Grebe patent is disclosed in Chamberlain, U.S. Pat. No. 2,258,001, Oct. 7, 1944. There too, a flexible drilling conduit is utilized which terminates in a bullet-shaped nozzle with multiple ports. An acid is discharged from the drillhead to cut through the formation. Advancing movement of the drillhead into the formation is controlled by means at the top of the well which counterbalances the weight of the conduit. There is no indication how the systems of Grebe or Chamberlain could maintain a precise horizontal direction in view of the flexibility of the pipe.
Other patents disclose radials without precise information as to the mode of producing the radials in the formation. For example, Anderson et al., U.S. Pat. No. 3,994,340, Nov. 30, 1976, discloses a radial for the injection of steam into viscous petroleum formation with a production well adajacent one end of the formation.
In Pisio et al., U.S. Pat. No. 4,020,901, May 3, 1977, a complex arrangement is disclosed which suggests that steam injection and production could be accomplished in a single well. There are no details disclosed regarding the well casing. However, it is of such a large size that it appears the technique is such that miners descend to a location near the bottom of the well to drill horizontal holes.
Granville, U.S. Pat. No. 1,367,042 discloses a flexible metal tube which is stated to turn at a right angle and with a rotating drill head at its forward end. A shaft 12 is included to rotate the drill. Such a shaft would tend to flail around inside the flexible tube to destroy it. It also limits the area at the drillhead against which fluid pressure may be applied. Another problem with Granville is that it requires the use of flexible tubing which would tend to buckle this. This leads to large frictional forces between the buckling flexible tube and rigid pipe. Also, there is metal to metal contact along the entire surface of rigid pipe 3. The total frictional forces would prevent the flexible pipe from moving forward to any significant extent.
In Dickinson et al. U.S. Pat. No. 4,527,639, a piston-like system is disclosed which permits the turning of rigid pipe through a short radius 90.degree. turn. This is accomplished by directing hydraulic fluid against the rearward side of a drillhead at the forward end of the drilling pipe to provide a "pulling" force at the drillhead to move the pipe into the formation without buckling of the pipe. The pipe moves through a seal in a surrounding guidepipe to permit the application of such forces which are sufficient to carry the drillhead and pipe through the short radius turn set forth above. The ability to use a rigid pipe is a major advance in that it avoids the buckling likely in a flexible pipe which, if it reached reached the formation, would tend to wander undirected to prevent the precise placement of radials.
The above system of U.S. Pat. No. 4,527,639, is a major advance over earlier prior art. It would be improved even further by the ability to provide additive forces in addition to the pulling forces which would assist in moving the rigid pipe through the whipstock long distances into the underground formation. Such additional forces could also be used to control the rate of movement of the radial pipe and to the formation.